Process of purifying technical sodium pyrosilicate hydrates



Patented Oct. 17, 1933' I #9? f. n t

PROCESS OF PURIFYING 7 TECHNICAL SODIUM PYROSILICATE HYDRATES i Myron C. Waddell, Lakewood, Ohio, assignorvto The Grasselli Chemical Company, Cleveland, Ohio, a corporation of Delaware No Drawing. Application October 25, 1932 7 Serial No. 639,535

Claims. rel. 23-110) My invention may be practiced for example as tions calculate in advance from the analytical follows: Sodium pyrosilicate hydrate crystals data of the raw, impure pyrosilicate and the are produced from solutions containing the treating liquor, the amount of water required to proper excess of caustic soda as disclosed in my produce a final deca or other desired hydrate.

5 above cited application. The crystals are sepa- I have shown in my co-pending application 5:

rated as completely as possible from their mother Ser. #639,534 filed on even date herewith that liquor, as by centrifuging. A solution of sodium novel crystalline sodium pyrosilicate hydrates of silicate of a ratio for instance lNa O: 28102.15 the composition NasSizOmXHzO, in which X is then mixed thoroughly, preferably by spraying, about 10, can be obtained by cooling. hot, concen- 10 Iwith the centrifuged crystals in such an amount trated solutions ofsodiumpyrosilicate containing 60-,

that the free caustic in the crystal mass is consubstantial amounts of free caustic alkali, 1.0. in verted to sodium pyrosilicate. The addition is excess to that corresponding to the pyrosilicate made slowly in order not to obtain a sticky, ratio of 3Naz0: 28102. The resulting crystals gummy mass. The loose, damp crystal mass is contain, however, due to contaminating, mother then dried in any suitable apparatus, preferably liquor, some free caustic alkali. This adhering. 651- by tumbling in a slow current of warm air. mother liquor causes difiiculty in drying the The crystals are then in a dry, free-flowing conpyrosilicate hydrate crystals and it is the aim of dition ready for packaging and storage. the present invention to free the crystals from As a specific example of how my invention has this free caustic alkali.

, been applied to the purification of a crude, crys- Y My invention relates therefor to the elimina- 70f talline pyrosilicate hydrate the following is tion of free caustic alkali contained in the given: mother liquor adhering to'the' sodium pyrosili- A crude, technical sodium pyrosilicate hydrate cate hydrate crystals obtained by crystallization was available which contained 37.1% NazO and of strongly alkaline pyrosilicate solutions and it 22.7% SiOz, this contained therefor 2.5% excess consists in neutralizing said free caustic and 75.

NaOH. 700 grams of this product were caretransforming it into pyrosilicate.- A veryconfully sprayed and thoroughly mixed with 58 venient manner of transforming said freecausgrams of a silicate solution containing 22.6% tie into pyrosilicate consists in treating "the S102 and 11.6% NazO, the mix was then air crude, technical pyrosilicate hydrate crystals dried rapidly, it gave a free-flowing product, with a predetermined amount of a sodium 'sili- 8011 showing an analysis 36.2% NazO and 24.1% S102, cate solution in which the ratio of SiOz to NazO or an excess of 1.1% S10; over the theoretical is eate than tha O the py a h q for pyrosilicate. solution contains more S102 than corresponds to From these analytical data, one obtains the the pyrosilicate ratio of v.3Na2O: 2Si02. Any

formula, of thi product as sodium silicate having a ratio of NazO: 510 -1-35;

from 1: 1 to as high as 1: 4 can be" used in my 3NaZO-2-O7S1O2'11-3H2O I process, but a silicate "of a 1:2 ratiohas been found particularly satisfactory. for this purpose since it has a high neutralizing value forth'e .pyrosilicate containing about 10 mols of water I w adsorbed caustic soda and 18 not too viscous to 90. of crystallization. .It W111 be understood that it mixv readily into the crystal mass; v

is quite impractical to produce on air drying 1 claim. 7 1 technical silicates which have the water content In a r f if i a technical, n' Prrespondmg exactly the formula 9 talline sodium pyrosilicate hydrate contaminated mte hydrate- Q practlcal Purposes thls 1s qulte With free caustic alkali, the step of transforming 951' unnecessary as e Products are mostly used in said freevalkali into sodium pyrosilicate hydrate; aqueous solutions. Keeping in mind that the 2, I ro of purifying a technical, crysa hydrate is the most a and p y the talline sodium pyrosilicate hydrate contaminated only definitely known pyrosilicate hydrate, one with free caustic alkali, the step of mixing said which corresponds closely to a more or less moist can easily by ordinary stoechiometric calculaproduct with a sodium silicate solution containv ing more SiOz than corresponds to the ratio 3Naz0: 28102. i

3. In a process of purifying a technical, crystalline sodium pyrosilicate hydrate contaminated with free caustic alkali, the step of mixing said product with asodium silicate solution of a composition and in an amount adjusted to transform said free alkali into sodium pyrosilicate.

4. In a process of purifying a technical, crys- I talline sodium pyrosilicate hydrate contaminated with free caustic alkali, the'steps of mixing said product with a sodium silicate solution containing more SiOz than corresponds to the ratio '3Naz0: ZSiOz, the amount and composition of said added silicate being adjusted to transform 7 

